Elementary physics question

[johnwandering]

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This is a very basic question, but i am having a hard time understanding this~~

A man in space pulls another on a rope. According to newtons law, there is equal and opposite reaction.
So why does the man move? Shouldnt his reactive force cancel out in theory (obviously i he does move)

BR says although rope and man exert equal opposite forces, when considering motion of mass, we only look at the forces acting on the mass.
I dont know why but this doesnt seem to make any sense to me.
So we just, completely ignore the reactive forces?

 

[milski]

The forces are acting on different bodies. The man is exerting a force on the rope and the rope moves. The rope is exerting a force on the man and the man also moves (on the ground there would be normally static friction force to cancel that). As a total the center of mass on the man and the rop stays stationary and their total momentum - constant. If the man is fast and strong and lets go when he reaches the end of his rope, they'll both fly away from each other while still maintaining that fixed center of mass.

 

[MedPR]

This is a very basic question, but i am having a hard time understanding this~~

A man in space pulls another on a rope. According to newtons law, there is equal and opposite reaction.
So why does the man move? Shouldnt his reactive force cancel out in theory (obviously i he does move)

BR says although rope and man exert equal opposite forces, when considering motion of mass, we only look at the forces acting on the mass.
I dont know why but this doesnt seem to make any sense to me.
So we just, completely ignore the reactive forces?

You have to pick a frame of reference. So you either look at the man, or you look at the rope.